The Rubber Industry primarily uses internal batch type mixers to mix baled polymer with preweighed compounding chemicals. The internal mixer action wedges the baled polymer between its two rotors and mixing chamber surfaces, smear and shearing the polymer progressively into smaller and smaller pieces, an operation which requires rugged equipment with high power input. This high power input heats the batch and limits the batch mixing time due to temperature. The finished batch is dropped onto a mill or into an extruder for sheeting or pelletizing and transfer to the next operation.
Limited use of continuous mixing is being performed by a unit combining the internal mixer with extruders. The unit consists of a dual rotor feed end, which resembles the internal mixer, with each rotor being formed into an extruder at its discharge end. A third extruder is placed at right angles to combine the output of the two rotors. As the feed end smears the baled polymer, heat is developed in the polymer before chemical additives are exposed to adequate polymer surface area to begin the mixing process. Thus the mixing quality is approximately the same as produced by the internal mixer and mills type of mixing line.